1. Field of the Invention
This invention relates generally to seals that are suitable for containing a pressurized fluid that may be abrasive, and for providing a film of lubricant at the dynamic sealing interface in response to relative rotation to enhance pressure and rotary speed capabilities.
The seals of the present invention are particularly suitable for use in rotary swivel assemblies, such as the general type of oilfield washpipe assemblies that are described in U.S. Pat. No. 2,764,428 entitled “Wash Pipe Mounting For Swivels,” IADC/SPE Paper 59107 “A New Hydrodynamic Washpipe Sealing System Extends Performance Envelope and Provides Economic Benefit,” and commonly assigned U.S. Pat. No. 6,007,105 entitled “Swivel Seal Assembly.”
2. Description of the Related Art
Rotary seals are used to establish sealing between relatively rotatable machine components, for the purpose of retaining a pressurized fluid. The type of sealing ring that is most commonly used in oilfield washpipe assemblies is typically referred to as washpipe packing, and dates at least to U.S. Pat. No. 2,394,800 entitled “Rotary Swivel.” Such conventional washpipe packing is used to retain pressurized drilling fluid. Differential pressure energizes the dynamic sealing lip against the washpipe. While this type of packing has served the oilfield for many years, it is not suitable for the higher speeds and pressures of today's deep wells. The problems and extreme expenses associated with failures of conventional packing in deep wells are described in IADC/SPE Paper 59107.
The antecedents to the packings used in many other types of applications are shown, for example, in U.S. Pat. No. 2,442,687 entitled “Packing For Stuffing Boxes” and U.S. Pat. No. 2,459,472 entitled “Rotary Swivel.”
In general, the term “packing” simply refers to a sealing ring that is intended to be used in a “stuffing box” of one sort or another. “Packing” and “stuffing box” are terms that date back to the 1770's, and perhaps earlier. A stuffing box is a housing with a deep cylindrical cavity that receives a plurality of packing rings. Some or all of the packing rings are often installed in abutting relation with spacer rings that perform a packing ring supporting function. For several examples of spacer/support rings, see the aforementioned U.S. Pat. Nos. 2,394,800, 2,442,687, and 2,459,472, and IADC/SPE Paper 59107.
Commonly assigned U.S. Pat. No. 6,334,619, entitled “Hydrodynamic Sealing Assembly,” shows a hydrodynamically lubricated packing ring assembly that has the disadvantage of requiring an expensive wavy backup ring.
Kalsi Engineering manufactures various configurations of hydrodynamic rotary seals, and sells them under the registered trademark “KALSI SEALS.” The factors involved in using such seals to contain a pressurized fluid are described in U.S. Pat. No. 6,334,619. Typical seal configurations require a lubricant pressure that is greater than, or nearly equal to, that of the contained fluid. To contain a highly pressurized fluid, one can use a pair of oppositely-facing seals; one to serve as a partition between the lubricant and the pressurized fluid, and the other to retain the lubricant, as described in conjunction with FIGS. 3-38 of the Kalsi Seals Handbook, Revision 1 (Kalsi Engineering, Inc. Document No. 2137 Revision 1, 2005). The lubricant is maintained at a pressure equal to or greater than that of the contained fluid. This scheme ensures that neither seal is exposed to a high differential pressure acting from the wrong side, but requires a special mechanism to maintain the lubricant pressure at or above that of the contained fluid.
Many applications, such as the oilfield drilling swivel, the progressive cavity artificial lift pump, centrifugal pumps, and rotary mining equipment, would benefit significantly from a hydrodynamically lubricated rotary packing ring seal having the ability to operate under conditions where pressure of the contained fluid is higher than the lubricant pressure.